Keeping pond fish is a very popular aquaculture production in the traditional aquaculture industry. Due to the increasingly lack of land and water resources, the cost of pond aquaculture keeps increasing at a rate in excess of inflation because of the low culture density and ever-declining economic benefits. A circulating water culture system with a filtration device is common practice in today's aquaculture applications. However, while an excessively large circulating water culture system allows higher density and intensive farming opportunities thus providing economic benefits, it also faces many challenges. In the process of adopting higher density farming operations, due to the need for excessive feeding, a large amount of residual feed and animal excrement produces pollutants such as ammonia nitrogen, nitrite and sulfide, which not only pollute the water but also negatively impact cultured animal health. These same problems are also encountered in most recirculating hobbyist ponds and display aquariums around the world.
With reference to water treatment in any recirculating aquaculture system, microorganisms, such as Bacillus, nitrifying bacteria, denitrifying bacteria, yeast, Lactobacillus, photosynthetic bacteria, are proliferated to degrade excess feed, waste, ammonia nitrogen, nitrite nitrogen, nitrate nitrogen and other organic and inorganic substances. Through the microbial activities of nitrogen fixation, dehydrogenation, carbon fixation and oxidation, the harmful substances in the water are transformed via the nitrogen cycle, significantly reducing the amount of ammonia nitrogen and nitrite as well as chemical oxygen demand (COD) of the water while working to stabilize the pH.
Most microorganisms induced to aid aquaculture water purification are directly sprayed or added, via liquid or powder form, to the water. However, these types of products offer no protection for the microorganisms, leaving the microbial cells to be flushed away by water flow, which leads to random and unpredictable growth of microbial cells on the filters or in the water. The desired and necessary benefit to help maintain the needed water quality thereby becomes unlikely due to the lack of microbial colonization at a specific location and as the microorganism colonies degrade over time the water filtration system loses efficiency and effectiveness. In addition, the nutrients contained in the prior art are not fully protected, some even completely exposed in the water. During the utilization of these products, harmful bacteria such as Escherichia coli, Vibrio have ready access to nutrients in the water column, eliminating the needed nutrients before the activation of sufficient colonies of microorganisms necessary for effective and efficient water purification, and thus results in an adverse proliferation of harmful microorganisms. Moreover, agents added to the microbial products such as calcium carbonate, zeolite powder, ceramsite, bentonite, diatomaceous earth, porous clay, porous volcanic rock and zeolite cannot be recycled, which causes secondary pollution of the water.
CN pat. No. 101264985B to Guo et al. discloses a sustained-release water treatment microorganism. Though the pores of natural ore particles provide the microorganisms and nutrients breeding grounds to attach and have certain sustained-release ability, the microorganisms are still flushed and diluted by water flow due to the absence of protection of the microorganisms. As long as the beneficial bacteria cannot form predominant bacterial flora, the aforementioned disadvantages cannot be overcome. CN pat. No. 206232700U to Lv et al. discloses a microorganism device having long-acting and slow-release properties for sewage treatment. However, there is no protection for the core of the device; furthermore, the microporous filter is a hollow cylinder open at both ends, which renders the internal core of the device negatively impacted by water flow and by bringing harmful bacteria into it, snatching and utilizing the nutrients required for beneficial bacteria. The beneficial bacteria are therefore not able to form predominant bacterial flora. Therefore, it is of great significance to provide a method for microorganisms, used for water purification, to colonize in a specific position, especially inside a filter, in a recirculating aquaculture system, so as to enhance the effectiveness of the filter.